fe-code-style

What I do

Diagnose and fix Java code style issues in the FE module using the project's Checkstyle configuration.

When to use me

• Before committing FE Java code changes
• When FE build fails due to checkstyle violations
• When you need to understand FE style rules

Procedure

Step 1: Run checkstyle

Checkstyle is integrated into the Maven build and runs automatically during mvn validate. To check style only (without full compilation):

cd fe && mvn checkstyle:check -pl fe-core

Or as part of the normal build:

./build.sh --fe -j${DORIS_PARALLELISM}

If checkstyle fails, the build will fail with error messages showing the file, line number, and rule violated.

Step 2: Interpret violations

Checkstyle output looks like:

[ERROR] src/main/java/.../Foo.java:[42:5] (imports) UnusedImports: Unused import - java.util.List.
[ERROR] src/main/java/.../Bar.java:[10] (header) RegexpHeader: Line does not match expected header line...

Each error shows: [file]:[line:col] (category) RuleName: description.

Step 3: Fix common violations

Violation	Fix
RegexpHeader	Add/fix Apache License header at file top
UnusedImports	Remove unused import statements
LineLength (>120 chars)	Break long lines
IllegalImport (shaded classes)	Use the non-shaded equivalent (see import-control.xml)
FileTabCharacter	Replace tabs with spaces
NewlineAtEndOfFile	Ensure file ends with a newline
MergeConflictMarker	Resolve git merge conflicts

Step 4: Verify fix

After fixing, re-run checkstyle to confirm:

cd fe && mvn checkstyle:check -pl fe-core

Key Configuration

File	Purpose
fe/check/checkstyle/checkstyle.xml	Main rules (license header, line length 120, encoding, imports)
fe/check/checkstyle/suppressions.xml	Rule exclusions (test files, nereids, large files)
fe/check/checkstyle/import-control.xml	Import restrictions (no shaded classes, no old logging APIs, no Lombok in nereids)
fe/check/checkstyle/checkstyle-apache-header.txt	Apache License 2.0 header template
build-support/IntelliJ-code-format.xml	IntelliJ formatter scheme (120 col, import organization)

Suppression Rules

Some files/packages have relaxed rules (see suppressions.xml):

• Test files: Javadoc rules suppressed
• Non-nereids code: Some strict rules suppressed
• Specific large files: Individual suppressions

Excluded Code

The following are excluded from checkstyle (see fe/pom.xml):

• **/apache/doris/thrift/**/* (generated Thrift code)
• **/apache/parquet/**/* (generated Parquet code)

Import Restrictions (key rules from import-control.xml)

• No shaded imports: Do not use org.apache.doris.thirdparty.* directly
• No old logging: Do not use org.apache.commons.logging or java.util.logging
• No SimpleDateFormat: Use java.time APIs instead
• No Lombok in nereids: lombok is disallowed in org.apache.doris.nereids package

Troubleshooting

Problem	Solution
Build fails on validate phase	Run mvn checkstyle:check -pl fe-core to see specific violations
Can't find checkstyle config	Ensure you're running from the fe/ directory
IntelliJ formatting differs	Import build-support/IntelliJ-code-format.xml via Settings → Editor → Code Style